In recent years, the amount information to be processed, stored, and communicated has increased significantly, creating a demand for high capacity information recording devices. In hard disk drive (HDD) technology, various technological advancements particularly those related to perpendicular magnetic recording have achieved a desired increase in a recording density. Configurations for discrete track and/or bit patterned magnetic media which provide an increase in the recording density and keep the effects of thermal fluctuations within acceptable tolerances have been proposed. Development of manufacturing technology to produce such proposed configurations is urgently needed.
In a pattern of magnetic cells in a medium, each magnetic cell needs to be magnetically separated from other cells to provide storage for one bit of information (data) in each cell of a bit patterned medium. Using microfabrication technology, magnetic cells (e.g., dot shaped areas) and nonmagnetic regions are often formed in the same plane of a medium. A method for selectively deactivating the magnetic property of selected portions the recording medium by injecting an ionized different-type element can be used to make the nonmagnetic regions. Microfabrication patterns are generally used in the process of creating such structures.
Specifically, semiconductor manufacturing patterning is performed to create a magnetic region and a nonmagnetic region on a magnetic recording layer of a substrate which are independent and separate. A mask for a patterning to transfer a fine protrusion-recess pattern is formed on a magnetic recording layer, and that particular protrusion-recess pattern is produced on a magnetic recording medium underlying the magnetic recording layer upon further selective material removal processes are used to remove material after the protrusion-recession pattern is provided thereon.
A general-purpose resist material as is commonly used in semiconductor manufacturing processes is used to create protrusions and recesses in the mask pattern. A methods to obtain desired resist patterns include selectively creating a pattern by using an irradiating energy beam and selectively patterning a self-assembling film containing a resist film in which a chemically different pattern (or arrangement) is used. Another method uses irradiation to inject high energy ions into the magnetic recording layer to deactivate magnetization portions of a pattern after the protrusion-recession is provided to a mask pattern, so that the pattern defines magnetically separate regions in the medium.
When a mask pattern remains on the magnetic recording layer, a protrusion part that forms a magnetic dot (region) creating a high area above adjacent structures which may cause a magnetic head performing writing or recording to the magnetic recording medium on the medium to crash. Also, when the distance between the magnetic recording layer and the magnetic head is large, a signal to noise (S/N) ratio of signals that can be detected by the magnetic head becomes small. Therefore, the height of the protrusion part above surrounding/adjacent structures should be minimized by removing the mask pattern on the magnetic recording layer after the patterning of the magnetic recording layer. A release layer is provided between the magnetic recording layer and the mask layer in a practical process. The mask layer is removed from the upper side of the magnetic recording layer by dissolving the release layer, and the planarity of the medium is improved (i.e., roughness is reduced), so that a favorable head to magnetic recording medium glide property is obtained.
In a stripping process of a bit patterned medium, in addition to a stripping method in which a carbon film is exposed in an oxygen plasma atmosphere and a dry etching is performed, there is also a stripping method in which a metal film is used as a release layer and a wet etching using an acid, etc. as a stripping solution is performed. In dry etching, unremoved particles remain after the mask process becomes a transfer mask, the unremoved particles also remain on the medium surface after the dry etch stripping process which contributes to a degradation of a head disk interface (HDI) property. On the other hand, in the wet etching, the unremoved particles are lifted off from the mask by dissolving the release layer, so the amount of residue on the medium surface is reduced and the HDI property is improved.
Because the release layer used in the wet stripping eventually becomes an under layer of the mask layer that is provided in a further upper portion, pattern size variation from layer to layer in subsequent processes is reduced. In order to maintain the planarity, it is desired that the surface roughness of the release layer be small.
On the other hand, it is necessary to transfer the protrusion-recess pattern to the release layer before the magnetic recording layer is processed. However, the mask layer at that time includes recesses, so subsequent processing requires tight process control, i.e., the allowable variation processing in subsequent processing of the magnetic recording layer is narrowed. Following the teachings of conventional technology, to obtain acceptable tolerances of the parameters for satisfactory process control and the desired stripping process performance, a method for adjusting the thickness of the release layer is proposed. However, while the recess depth of the processed mask is reduced when the release layer is made thinner, the contact area on which the stripping solution acts is reduced, so that the amount of residue left after the stripping is increased. In contrast, when the film thickness of the release layer is thickened, the contact area available is increases and the stripping process efficiency is improved. However, the range of process variation to achieve acceptable processing of the thick release layer becomes narrow, and also the pattern size variation, which is caused by an increase in the surface roughness, becomes large. Therefore, an adjustment of the thickness of the release layer does not result in a satisfactory solution to the challenge of transferring a fine pattern of the release layer and performing the specified layer stripping process, therefore, it is desired to improve the processability, the stripping property, and the planarity of the release layer.